Aptamer delivery of siRNA, radiopharmaceutics and chemotherapy agents in cancer

Molecular elements: novel approaches for molecular building

Classically, a molecular element (ME) is a pure substance composed of two or more atoms of the same element. However, MEs, in the context of this review, can be any molecules as elements bonded together into the backbone of synthetic oligonucleotides (ONs) with designed sequences and functions, including natural A, T, C, G, U, and unnatural bases. The use of MEs can facilitate the synthesis of designer molecules and smart materials. In particular, we discuss the landmarks associated with DNA structure and related technologies, as well as the extensive application of ONs, the ideal type of molecules for intervention therapy aimed at correcting disease-causing genetic errors (indels). It is herein concluded that the discovery of ON therapeutics and the fabrication of designer molecules or nanostructures depend on the ME concept that we previously published. Accordingly, ME will be our focal point as we discuss related research directions and perspectives in making molecules and materials. This article is part of the theme issue 'Reactivity and mechanism in chemical and synthetic biology'.

Anti-cancer therapeutic strategies based on HGF/MET, EpCAM, and tumor-stromal cross talk

As an intelligent disease, tumors apply several pathways to evade the immune system. It can use alternative routes to bypass intracellular signaling pathways, such as nuclear factor-κB (NF-κB), Wnt, and mitogen-activated protein (MAP)/phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR). Therefore, these mechanisms lead to therapeutic resistance in cancer. Also, these pathways play important roles in the proliferation, survival, migration, and invasion of cells. In most cancers, these signaling pathways are overactivated, caused by mutation, overexpression, etc. Since numerous molecules share these signaling pathways, the identification of key molecules is crucial to achieve favorable consequences in cancer therapy. One of the key molecules is the mesenchymal-epithelial transition factor (MET; c-Met) and its ligand hepatocyte growth factor (HGF). Another molecule is the epithelial cell adhesion molecule (EpCAM), which its binding is hemophilic. Although both of them are involved in many physiologic processes (especially in embryonic stages), in some cancers, they are overexpressed on epithelial cells. Since they share intracellular pathways, targeting them simultaneously may inhibit substitute pathways that tumor uses to evade the immune system and resistant to therapeutic agents.

Glioblastoma: Current Status, Emerging Targets, and Recent Advances

Glioblastoma (GBM) is a highly malignant brain tumor characterized by a heterogeneous population of genetically unstable and highly infiltrative cells that are resistant to chemotherapy. Although substantial efforts have been invested in the field of anti-GBM drug discovery in the past decade, success has primarily been confined to the preclinical level, and clinical studies have often been hampered due to efficacy-, selectivity-, or physicochemical property-related issues. Thus, expansion of the list of molecular targets coupled with a pragmatic design of new small-molecule inhibitors with central nervous system (CNS)-penetrating ability is required to steer the wheels of anti-GBM drug discovery endeavors. This Perspective presents various aspects of drug discovery (challenges in GBM drug discovery and delivery, therapeutic targets, and agents under clinical investigation). The comprehensively covered sections include the recent medicinal chemistry campaigns embarked upon to validate the potential of numerous enzymes/proteins/receptors as therapeutic targets in GBM.

Progress in cancer drug delivery based on AS1411 oriented nanomaterials

Targeted cancer therapy has become one of the most important medical methods because of the spreading and metastatic nature of cancer. Based on the introduction of AS1411 and its four-chain structure, this paper reviews the research progress in cancer detection and drug delivery systems by modifying AS1411 aptamers based on graphene, mesoporous silica, silver and gold. The application of AS1411 in cancer treatment and drug delivery and the use of AS1411 as a targeting agent for the detection of cancer markers such as nucleoli were summarized from three aspects of active targeting, passive targeting and targeted nucleic acid apharmers. Although AS1411 has been withdrawn from clinical trials, the research surrounding its structural optimization is still very popular. Further progress has been made in the modification of nanoparticles loaded with TCM extracts by AS1411.

Simultaneous nanocarrier-mediated delivery of siRNAs and chemotherapeutic agents in cancer therapy and diagnosis: Recent advances

Recently, investigations have revealed that RNA interference (RNAi) has a remarkable potential to decrease cancer burden by downregulating genes. Among various RNAi molecules, small interfering RNA (siRNA) has been more attractive for this goal and is able to silence a target pathological path and promote the degradation of a certain mRNA, resulting in either gain or loss of function of proteins. Moreover, therapeutic siRNAs have exhibited low side effects compared to other therapeutic molecular candidates. Nevertheless, siRNA delivery has its own limitations including quick degradation in circulation, ineffective internalization and low passive uptake by cells, possible toxicity against off-target sites, and inducing unfavorable immune responses. Therefore, delivery tools must be able to specifically direct siRNAs to their target locations without inflicting detrimental effects on other sites. To conquer the mentioned problems, nanocarrier-mediated delivery of siRNAs, using inorganic nanoparticles (NPs), polymers, and lipids, has been developed as a biocompatible delivery approach. In this review, we have discussed recent advances in the siRNA delivery methods that employ nanoparticles, lipids, and polymers, as well as the inorganic-based co-delivery systems used to deliver siRNAs and anticancer agents to target cells.

Aptamer Applications in Neuroscience

Being the predominant cause of disability, neurological diseases have received much attention from the global health community. Over a billion people suffer from one of the following neurological disorders: dementia, epilepsy, stroke, migraine, meningitis, Alzheimer's disease, Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis, Huntington's disease, prion disease, or brain tumors. The diagnosis and treatment options are limited for many of these diseases. Aptamers, being small and non-immunogenic nucleic acid molecules that are easy to chemically modify, offer potential diagnostic and theragnostic applications to meet these needs. This review covers pioneering studies in applying aptamers, which shows promise for future diagnostics and treatments of neurological disorders that pose increasingly dire worldwide health challenges.

MUC1-Targeted Radiopharmaceuticals in Cancer Imaging and Therapy

Mucin 1 (MUC1) is a large, transmembrane mucin glycoprotein overexpressed in most adenocarcinomas and plays an important role in tumor progression. Regarding its cellular distribution, biochemical features, and function, tumor-related MUC1 varies from the MUC1 expressed in normal cells. Therefore, targeting MUC1 for cancer immunotherapy and imaging can exploit the difference between cancerous and normal cells. Radiopharmaceuticals have a potential use as carriers for the delivery of radionuclides to tumors for a diagnostic imaging and radiotherapy. Several radiolabeled targeting molecules like peptides, antibodies, and aptamers have been efficiently demonstrated in detecting and treating cancer by targeting MUC1. This review provides a brief overview of the current status of developments and applications of MUC1-targeted radiopharmaceuticals in cancer imaging and therapy.

Aptamers: a novel targeted theranostic platform for pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is an extremely challenging disease with a high mortality rate and a short overall survival time. The poor prognosis can be explained by aggressive tumor growth, late diagnosis, and therapy resistance. Consistent efforts have been made focusing on early tumor detection and novel drug development. Various strategies aim at increasing target specificity or local enrichment of chemotherapeutics as well as imaging agents in tumor tissue. Aptamers have the potential to provide early detection and permit anti-cancer therapy with significantly reduced side effects. These molecules are in-vitro selected single-stranded oligonucleotides that form stable three-dimensional structures. They are capable of binding to a variety of molecular targets with high affinity and specificity. Several properties such as high binding affinity, the in vitro chemical process of selection, a variety of chemical modifications of molecular platforms for diverse function, non-immunoreactivity, modification of bioavailability, and manipulation of pharmacokinetics make aptamers attractive targets compared to conventional cell-specific ligands. To explore the potential of aptamers for early diagnosis and targeted therapy of PDAC - as single agents and in combination with radiotherapy - we summarize the generation process of aptamers and their application as biosensors, biomarker detection tools, targeted imaging tracers, and drug-delivery carriers. We are furthermore discussing the current implementation aptamers in clinical trials, their limitations and possible future utilization.

Functionalized selenium nanoparticles for targeted siRNA delivery silence Derlin1 and promote antitumor efficacy against cervical cancer

Small interfering RNA (siRNA) exhibits great potential as a novel therapeutic option due to its highly sequence-specific ability to silence genes. However, efficient and safe delivery carriers are required for developing novel therapeutic paradigms. Thus, the successful development of efficient delivery platforms for siRNA is a crucial issue for the development of siRNA-based drugs in cancer treatments. In this study, biocompatible selenium nanoparticles (SeNPs) were loaded with RGDfC peptide to fabricate tumor-targeting gene delivery vehicle RGDfC-SeNPs. Subsequently, RGDfC-SeNPs were loaded with Derlin1-siRNA to fabricate RGDfC-Se@siRNA, which are functionalized selenium nanoparticles. RGDfC-Se@siRNA showed greater uptake in HeLa cervical cancer cells in comparison with that in human umbilical vein endothelial cells (HUVECs), verifying the RGDfC-mediated specific uptake of RGDfC-Se@siRNA. RGDfC-Se@siRNA was capable of entering HeLa cells via clathrin-associated endocytosis, and showed faster siRNA release in a cancer cell microenvironment in comparison with a normal physiological environment. qPCR and western blotting assays both indicated that RGDfC-Se@siRNA exhibited an obvious gene silencing efficacy in HeLa cells. RGDfC-Se@siRNA suppressed the invasion, migration and the proliferation of HeLa cells, and triggered HeLa cell apoptosis. Moreover, RGDfC-Se@siRNA induced the disruption of mitochondrial membrane potentials. Meanwhile, RGDfC-Se@siRNA enhanced the generation of reactive oxygen species (ROS) in HeLa cell, suggesting that mitochondrial dysfunction mediated by ROS might play a significant role in RGDfC-Se@siRNA-induced apoptosis. Interestingly, RGDfC-SeNPs@siRNA exhibited significant antitumor activity in a HeLa tumor-bearing mouse model. Additionally, RGDfC-SeNPs@siRNA is nontoxic to main organ of mouse. The above results indicate that RGDfC-Se@siRNA provides a promising potential for cervical cancer therapy.

Combined Targeting of Glioblastoma Stem-Like Cells by Neutralizing RNA-Bio-Drugs for STAT3

An important drawback in the management of glioblastoma (GBM) patients is the frequent relapse upon surgery and therapy. A likely explanation is that conventional therapies poorly affect a small population of stem-like cancer cells (glioblastoma stem cells, GSCs) that remain capable of repopulating the tumour mass. Indeed, the development of therapeutic strategies able to hit GSCs while reducing the tumour burden has become an important challenge to increase a patient’s survival. The signal transducer and activator of transcription-3 (STAT3) has been reported to play a pivotal role in maintaining the tumour initiating capacity of the GSC population. Therefore, in order to impair the renewal and propagation of the PDGFRβ-expressing GSC population, here we took advantage of the aptamer–siRNA chimera (AsiC), named Gint4.T-STAT3, that we previously have shown to efficiently antagonize STAT3 in subcutaneous PDGFRβ-positive GBM xenografts. We demonstrate that the aptamer conjugate is able to effectively and specifically prevent patient-derived GSC function and expansion. Moreover, because of the therapeutic potential of using miR-10b inhibitors and of the broad expression of the Axl receptor in GBM, we used the GL21.T anti-Axl aptamer as the targeting moiety for anti-miR-10b, showing that, in combination with the STAT3 AsiC, the aptamer–miR-10b antagonist treatment further enhances the inhibition of GSC sphere formation. Our results highlight the potential to use a combined approach with targeted RNA therapeutics to inhibit GBM tumour dissemination and relapse.

Aptamers, the Nucleic Acid Antibodies, in Cancer Therapy

The arrival of the monoclonal antibody (mAb) technology in the 1970s brought with it the hope of conquering cancers to the medical community. However, mAbs, on the whole, did not achieve the expected wonder in cancer therapy although they do have demonstrated successfulness in the treatment of a few types of cancers. In 1990, another technology of making biomolecules capable of specific binding appeared. This technique, systematic evolution of ligands by exponential enrichment (SELEX), can make aptamers, single-stranded DNAs or RNAs that bind targets with high specificity and affinity. Aptamers have some advantages over mAbs in therapeutic uses particularly because they have little or no immunogenicity, which means the feasibility of repeated use and fewer side effects. In this review, the general properties of the aptamer, the advantages and limitations of aptamers, the principle and procedure of aptamer production with SELEX, particularly the undergoing studies in aptamers for cancer therapy, and selected anticancer aptamers that have entered clinical trials or are under active investigations are summarized.

Targeted siRNA Delivery Using Lipid Nanoparticles

Efficient intracellular delivery of small-interfering ribonucleic acid (siRNA) to the target organ or tissues in the body is assumed as the main hurdle for a widespread use of siRNAs in the clinics. Solid lipid-based nanoparticles (SLNs) and derivatives can potentially fit this purpose by enabling to overcome the extracellular and intracellular physiological barriers affecting the delivery. For that, rational formulations and rational process designs are needed. This chapter addresses a comprehensive description and critical appraisal of the main production methods of this particular type of lipid nanoparticles and the leading strategies to prompt a targeted delivery of siRNA.

Aptamers as Delivery Agents of siRNA and Chimeric Formulations for the Treatment of Cancer

Both aptamers and siRNA technologies have now reached maturity, and both have been validated with a product in the market. However, although pegaptanib reached the market some time ago, there has been a slow process for new aptamers to follow. Today, some 40 aptamers are in the market, but many in combination with siRNAs, in the form of specific delivery agents. This combination offers the potential to explore the high affinity and specificity of aptamers, the silencing power of siRNA, and, at times, the cytotoxicity of chemotherapy molecules in powerful combinations that promise to delivery new and potent therapies. In this review, we report new developments in the field, following up from our previous work, more specifically on the use of aptamers as delivery agents of siRNA in nanoparticle formulations, alone or in combination with chemotherapy, for the treatment of cancer.

Current Transport Systems and Clinical Applications for Small Interfering RNA (siRNA) Drugs

Small interfering RNAs (siRNAs) are an attractive new agent with potential as a therapeutic tool because of its ability to inhibit specific genes for many conditions, including viral infections and cancers. However, despite this potential, many challenges remain, including off-target effects, difficulties with delivery, immune responses, and toxicity. Traditional genetic vectors do not guarantee that siRNAs will silence genes in vivo. Rational design strategies, such as chemical modification, viral vectors, and non-viral vectors, including cationic liposomes, polymers, nanocarriers, and bioconjugated siRNAs, provide important opportunities to overcome these challenges. We summarize the results of research into vector delivery of siRNAs as a therapeutic agent from their design to clinical trials in ophthalmic diseases, cancers, respiratory diseases, and liver virus infections. Finally, we discuss the current state of siRNA delivery methods and the need for greater understanding of the requirements.

Signal Transducer and Activator of Transcription (STATs) Proteins in Cancer and Inflammation: Functions and Therapeutic Implication

Signal Transducer and Activator of Transcription (STAT) pathway is connected upstream with Janus kinases (JAK) family protein and capable of integrating inputs from different signaling pathways. Each family member plays unique functions in signal transduction and crucial in mediating cellular responses to different kind of cytokines. STAT family members notably STAT3 and STAT5 have been involved in cancer progression whereas STAT1 plays opposite role by suppressing tumor growth. Persistent STAT3/5 activation is known to promote chronic inflammation, which increases susceptibility of healthy cells to carcinogenesis. Here, we review the role of STATs in cancers and inflammation while discussing current therapeutic implications in different cancers and test models, especially the delivery of STAT3/5 targeting siRNA using nanoparticulate delivery system.

Advances in targeted nanotherapeutics: From bioconjugation to biomimicry

Since the emergence of cancer nanomedicine, researchers have had intense interest in developing nanoparticles (NPs) that can specifically target diseased sites while avoiding healthy tissue to mitigate the off-target effects seen with conventional treatments like chemotherapy. Initial endeavors focused on the bioconjugation of targeting agents to NPs, and more recently, researchers have begun to develop biomimetic NP platforms that can avoid immune recognition to maximally accumulate in tumors. In this review, we describe the advantages and limitations of each of these targeting strategies. First, we review developments in bioconjugation strategies, where NPs are coated with biomolecules such as antibodies, aptamers, peptides, and small molecules to enable cell-specific binding. While bioconjugated NPs offer many exciting features and have improved pharmacokinetics and biodistribution relative to unmodified NPs, they are still recognized by the body as "foreign", resulting in their clearance by the mononuclear phagocytic system (MPS). To overcome this limitation, researchers have recently begun to investigate biomimetic approaches that can hide NPs from immune recognition and reduce clearance by the MPS. These biomimetic NPs fall into two distinct categories: synthetic NPs that present naturally occurring structures, and NPs that are completely disguised by natural structures. Overall, bioconjugated and biomimetic NPs have substantial potential to improve upon conventional treatments by reducing off-target effects through site-specific delivery, and they show great promise for future standards of care. Here, we provide a summary of each strategy, discuss considerations for their design moving forward, and highlight their potential clinical impact on cancer therapy.

Molecular Application of Aptamers in the Diagnosis and Treatment of Cancer and Communicable Diseases

Cancer and infectious diseases such as Ebola, HIV, tuberculosis, Zika, hepatitis, measles and human schistosomiasis are serious global health hazards. The increasing annual morbidities and mortalities of these diseases have been blamed on drug resistance and the inefficacy of available diagnostic tools, particularly those which are immunologically-based. Antibody-based tools rely solely on antibody production for diagnosis and for this reason they are the major cause of diagnostic delays. Unfortunately, the control of these diseases depends on early detection and administration of effective treatment therefore any diagnostic delay is a huge challenge to curbing these diseases. Hence, there is a need for alternative diagnostic tools, discovery and development of novel therapeutic agents. Studies have demonstrated that aptamers could potentially offer one of the best solutions to these problems. Aptamers are short sequences of either DNA or RNA molecules, which are identified in vitro through a SELEX process. They are sensitive and bind specifically to target molecules. Their promising features suggest they may serve as better diagnostic agents and can be used as drug carriers for therapeutic purposes. In this article, we review the applications of aptamers in the theranostics of cancer and some infectious diseases.

Covalent Strategies for Targeting Messenger and Non-Coding RNAs: An Updated Review on siRNA, miRNA and antimiR Conjugates

Oligonucleotide-based therapy has become an alternative to classical approaches in the search of novel therapeutics involving gene-related diseases. Several mechanisms have been described in which demonstrate the pivotal role of oligonucleotide for modulating gene expression. Antisense oligonucleotides (ASOs) and more recently siRNAs and miRNAs have made important contributions either in reducing aberrant protein levels by sequence-specific targeting messenger RNAs (mRNAs) or restoring the anomalous levels of non-coding RNAs (ncRNAs) that are involved in a good number of diseases including cancer. In addition to formulation approaches which have contributed to accelerate the presence of ASOs, siRNAs and miRNAs in clinical trials; the covalent linkage between non-viral vectors and nucleic acids has also added value and opened new perspectives to the development of promising nucleic acid-based therapeutics. This review article is mainly focused on the strategies carried out for covalently modifying siRNA and miRNA molecules. Examples involving cell-penetrating peptides (CPPs), carbohydrates, polymers, lipids and aptamers are discussed for the synthesis of siRNA conjugates whereas in the case of miRNA-based drugs, this review article makes special emphasis in using antagomiRs, locked nucleic acids (LNAs), peptide nucleic acids (PNAs) as well as nanoparticles. The biomedical applications of siRNA and miRNA conjugates are also discussed.

EpCAM Immunotherapy versus Specific Targeted Delivery of Drugs

The epithelial cell adhesion molecule (EpCAM), or CD326, was one of the first cancer associated biomarkers to be discovered. In the last forty years, this biomarker has been investigated for use in personalized cancer therapy, with the first monoclonal antibody, edrecolomab, being trialled in humans more than thirty years ago. Since then, several other monoclonal antibodies have been raised to EpCAM and tested in clinical trials. However, while monoclonal antibody therapy has been investigated against EpCAM for almost 40 years as primary or adjuvant therapy, it has not shown as much promise as initially heralded. In this review, we look at the reasons why and consider alternative targeting options, such as aptamers, to turn this almost ubiquitously expressed epithelial cancer biomarker into a viable target for future personalized therapy.

Derivatizations of Sgc8-c aptamer to prepare metallic radiopharmaceuticals as imaging diagnostic agents: Syntheses, isolations, and physicochemical characterizations

Aptamers, oligonucleotides with the capability to bind to a target through non-covalent bonds with high affinity and specificity, have a great number of advantages as scaffold to prepare molecular imaging agents. In this sense, we have performed post-SELEX modifications of a truncated aptamer, Sgc8-c, which bind to protein tyrosine kinase 7 to obtain a specific molecular targeting probe for in vivo diagnosis and in vivo therapy. Herein, we describe the synthetic efforts to prepare conjugates between Sgc8-c and different metallic ions chelator moieties in short times, high purities, and adequate yields. The selected chelator moieties, derived from 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid, 2-benzyl-1,4,7-triazacyclononane-1,4,7-triacetic acid, and 6-hydrazinonicotinic acid, were covalently attached at the 5'-aptamer position yielding the expected products which were stable in aqueous solution up to 75°C and in typical aptamer storage conditions at least for 30 days.